1. Field of the Invention
This invention relates to a quantitative pipette capable of supplying repeatedly a fixed amount of a sample solution to a chemical analytical slide or the like.
2. Description of the Prior Art
Recently, clinical chemical assays through a dry process have widely been utilized because of their superiorities in the simplicity of analytical operation and in the rapidity of measurement. In the clinical chemical assay, a specific component in a liquid sample, such as glucose, urea nitrogen (BUN) or the like in blood, is analyzed quantitatively by spotting the sample onto a chemical analytical slide containing a reagent reacting with the above component, and measuring the coloration, discoloration or the like produced through the coloration, between the reagent and the specific component.
Heretofore, a prescribed amount of the sample was sucked with a pipette, and a round droplet was allowed to form at the lower end of the tip of the pipette. Then, the droplet was spotted in the central portion of the chemical analytical slide by touching it lightly with the surface.
However, in the above conventional spotting method, personal error in the spotted amount was noticeable, since the spotting work was carried out by operator's hand. A principal cause of the personal error was due to the difficulty in the keeping of a constant distance between the tip of the pipette and the spot face of the chemical analytical slide during the spotting. If a holder is used for supporting a pipette, the above personal error should be decreased. However, in this case, since the distance between the tip of the pipette and the spot face of the chemical analytical slide is fixed, it is impossible during a serial operation to form a droplet on the tip and subsequently to spot it to the spot face of the chemical analytical slide. On the other hand, there are various sample liquids to be assayed by chemical analytical slides, such as whole blood, blood plasma, blood serum, their diluted solutions, urine and saliva, and their absorption rates into the liquid-receiving layer, usually spreading layer on chemical analytical slides, are different from each other because of the differences in viscosity and the like. When the discharge rate from the pipette is too fast, a part of the droplet remains on and around the periphery of the tip resulting in an error of the spotted amount. Besides, in conventional pipettes, a total amount of a liquid sample sucked in the pipette is discharged at once. As a result, since suction and discharge should be repeated alternately, analytical work is troublesome. Some conventional pipettes can discharge the sucked sample by installments, however, PG,4 such pipettes are inferior in accuracy.